Sealing glass compositions containing calcined zirconia vanadia silica stain

ABSTRACT

Novel compositions of matter consisting of thermally crystallizable lead borosilicate and lead-zinc-borate sealing glasses having homogeneously blended therein a calcined zirconia vanadia silica stain.

United States Patent 1 Ellis June 10, 1975 SEALING GLASS COMPOSITIONS CONTAINING CALCINED ZIRCONIA VANADIA SILICA STAIN [75] Inventor: James L. Ellis, Toledo, Ohio [73] Assignee: Owens-Illinois, Inc., Toledo, Ohio [22] Filed: June 19, 1972 [2]] Appl. No.: 277,457

Related U.S. Application Data [63] Continuation of Ser. No. 831,648, June 6, 1969,

abandoned.

[52] U.S. Cl 106/53; 106/47 R; lO6/39.6;

106/54 [51] Int. Cl CO3c 3/10; CO3c 3/30; CO3c 3/22 [58] Field of Search 106/39.6, 299, 47, 53

[56] References Cited UNITED STATES PATENTS 2,889,952 6/1959 Claypoole lO6/39.6

Primary ExaminerWinston A. Douglas Assistant ExaminerMark Bell Attorney, Agent, or FirmRichard B. Dence; E. J. Holler [57] ABSTRACT Novel compositions of matter consisting of thermally crystallizable lead borosilicate and lead-zinc-borate sealing glasses having homogeneously blended therein a calcined zirconia vanadia silica stain.

4 Claims, 2 Drawing Figures PATENTEDJUH 10 I975 SHEET EIN F l m m w mmm DAL

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C @nw @mv@ 0 mwwmmwwwmw wmw mmSO wz3 wm 2- 20 wmmK n: Oo 20 mZwh m a mmmwcm 44mm com GALCINED STAIN INVENTOR. dAmes Lima BY X z. ,0. w Aware ees SEALING GLASS COMPOSITIONS CONTAINING CALCINED ZIRCONIA VANADIA SILICA STAIN This is a continuation of application Ser. No. 831,648, filed June 9, 1969, and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to novel compositions of matter, and more particularly, the subject invention concerns improved glass sealing compositions suitable for effectively assembling preformed component parts into a composite article of manufacture. Specifically, the instant invention pertains to new and unobvious thermally devitrifiable sealing glasses characterized by improved properties which make the sealing glasses suitable for fabricating items of commerce and science like cathode ray tubes, electronic components, encapsulated diodes without any apparent distortion or any deleterious effects on said item of commerce and science.

At present, the sealing glasses available to the art for joining preformed parts into a unitary composite item generally possess pronounced undesirable properties that often lead to serious fabrication problems. For example, the prior art sealing glasses may cure only at elevated temperatures and over an extended time, which curing property may lead to distortion of the joinable glass or glass ceramic parts or to physical damage to heat sensitive electronic components housed within a preformed glass structure. A further problem often evident in the prior art of sealing glasses is the poor flow for the sealing glasses. The poor flow of the sealing glass over the joinable surfaces or edges of the glass, ceramic or metal parts may prevent the intimate formation of an acceptable strong union of said parts. Also, of particular concern is the need for compatible thermal coefficient or expansion between the sealing glasses and the surfaces being sealed into a composite article. This latter property is important because, if the coefficients of the parts and the sealing glass are imcompatible, the resultant will be an unacceptable mismatch and a concurrent failure as often exhibited by strain or the like of the parts fused intimately one to the other.

There is a serious need for acceptable and workable sealing glass compositions for joining a number of important glasses, ceramics and metals for electronic use in the fields of both commerce and science. It will be appreciated by those skilled in the art to which the instant invention pertains that if novel and unobvious sealing glass compositions having acceptable and workable properties are made available to the art, the presence of said sealing compositions would represent a substantial contribution and advancement to the art.

Accordingly, it is an object of the present invention to provide new and improved sealing glass compositions.

Another object of the instant invention is to provide novel sealing glass compositions that have desirable chemical and physical properties.

Yet a still further object of the subject invention is to produce sealing glass compositions having acceptable workable properties for fabricating electronic items.

A still further object of the invention is to provide sealing glasses that have an improved cure temperature and an improved cure time, coupled with suitable flow and an acceptable coefficient of thermal expansion.

It is a further object of the present invention to overcome the difficulties associated with the prior art.

Other objects, features and advantages of this invention will become evident from the following detailed description of the mode and manner of practicing the invention.

SUMMARY OF THE INVENTION This invention concerns novel sealing glass compositions wherein said compositions comprise a thermally crystallizable solder sealing glass of the lead-zincborate or lead borosilicate type, having blended therein 2 to 18% of a calcined zirconia vanadia silica stain. The novel sealing glass possesses desirable properties for making glass-to-glass, glass-to-metal, glass-to-ceramic, ceramic-to-metal fusion type seals and the like.

DESCRIPTION OF THE INVENTION In attaining the objects of this invention, it has now been unexpectedly found that the subject sealing glasses with the desired flow, expansion and curing properties can be obtained by employing glass sealing compositions containing silicon oxide (SiO boric oxide (B 0 lead oxide (PbO), aluminum oxide (Al- O copper oxide (CuO), zinc oxide (ZnO), alkali oxide (M 0) wherein the alkali is sodium, potassium or lithium and the like glass forming oxides, having homogeneously and intimately dispersed therein calcined zirconia vanadia silica (ZrO SiO V 0 stain, in an intimate inventive combination of these components to produce sealing glass compositions with good sealing properties.

Exemplary of sealing glass compositions to which the calcined zirconia vanadia silica stain compound can be added are a devitrifiable lead-zinc-borate sealing glass consisting essentially of to weight percent PbO, 6 to 15 weight percent ZnO, 7 to 10 weight percent B 0 and about 0 to 5 weight percent SiO usually about 1 to 3 weight percent SiO Another lead-zincborate sealing glass suitable for use herein consists of 70 to 85 weight percent PbO, 6 to 15 weight percent ZnO, 7 to 10 weight percent B 0 1 to 5 weight percent SiO and l to 5 weight percent BaO; a leadborate sealing glass consisting of 70 to 85 weight percent PbO, 7 to 15 weight percent B 0 2 to 10 weight percent SiO and l to 5 weight percent A1 0 These base sealing glasses have a coefficient of expansion in the general range of l00l 15 X l0 /C (0300C). The glasses may also contain other glass-forming oxides such as Na O, K 0, CuO, SnO CaO and similar fluxes, colorants and the like. The sealing glasses as set forth supra usually contain homogeneously and intimately dispersed through about 2 to 18 weight percent calcined zirconia vanadia silica stain, with the presently preferred range of 5 to 12 weight percent. Generally, the linear thermal coefficient of expansion for the subject base sealing glasses will be lowered about 5 to 20 X 10 "/C (0300C) from the subject modified glass composition.

The novel sealing glasses of the disclosed compositional range can easily be prepared by employing tech niques known to the art. For example, when small batches are formulated, the batch ingredients are intimately mixed by hand, or for larger batches, the ingredients are mixed in a commercially available blender. After the ingredients are homogeneously blended, they are heated to such temperature so that all of the glassforming substances are present in the liquid state, thereby enabling the formation of a sealing glass from a homogeneous melt.

Generally, the batch ingredients were mixed well by hand and melting was done in a 90% platinum rhodium crucible heated in an electric furnace in an air atmosphere. Often, a slight amount of oxygen may be present in the melting furnace, usually about 0.5% of 0 The batch ingredients were continuously stirred during the melting and heating procedure.

The batch materials employed for preparing the sealing glasses of the invention were of high purity and they were selected from the following commercially available materials: SiO Kona Quintus Quartz, or Ottawa Sand; PbO, lead silicate (85 percent PbO, percent SiO or red lead; B 0 anhydrous boric oxide; ZnO, zinc oxide; K 0, potash or potassium carbonate; CuO, cupric oxide; A1 0 alumina and the like. Of course, the materials of the present invention may be in the form of functionally equivalent oxides, carbonates, fluorides, silicates, or any other form which does not disturb or adversely affect the subject glass composition.

The calcined zirconia vanadia silica stain employed herein can be easily obtained from commercial sources or it can be prepared by procedures well lmown to the art. One method for the preparation of calcined zirconia vanadia silica stain employs calcining a mixture of zirconium oxide, silicon and vanadium oxide wherein the zirconium oxide is present in the proportion from 0.8 to 8.5 times the weight of the silica and the vanadium oxide being present in proportions from 3 to 10.5% of the combined weight of zirconium oxide and silica. The mixture is calcinated at a temperature between 550 and 1300C. The procedure described immediately above is set forth in British Pat. No. 625,448. Other procedures for the preparation of calcinated stains of the type used herein are set forth in US. Pat.

The following examples are representative of embodiments of sealing glass compositions of the present invention and these examples are not to be construed as limiting as other obvious embodiments will be readily apparent to those versed in the art.

EXAMPLE 1 A sealing glass composition having a theoretical analysis of 2.3 weight percent SiO 7.7 weight percent B 0 0.5 weight percent K 0, 10.0 weight percent ZnO and 79.5 weight percent PbO was prepared by homogeneously and intimately blending 58 grams of commercially available Ottawa Sand No. 290, 18.4 grams of potash, 2023 grams of red lead, 196 grams of boric anhydride and 252 grams of zinc oxide. The substantially homogeneous mixture was melted in an electrically heated furnace in a platinum crucible. The melting and fining procedures were conducted at 2200F. for about 25 minutes. Thereafter, the glass was poured out of the container and fritted in a conventional manner. This glass, in the devitrified state, has a coefficient of expansion of about 113 X 10 /C (0-300C.).

EXAMPLE 2 A novel sealing glass composition of this invention was next prepared as follows: to 100 grams of the ground sealing glass prepared according to Example 1 was added 8 grams of calcined zirconia vanadia silica stain. The mixture of the sealing glass and calcined stain were thoroughly and homogeneously blended in a commercially available V-blender until an intimate mixture (usually about 1 hour) was obtained for the respective components. The commercially available calcined zirconia vanadia silica stain suitable for use herein generally contains 25 to 40 weight percent SiO 55 to weight percent ZrO and 2 to 10 weight percent V O The calcined stain used in this example was obtained from the l-larshaw Chemical Company and it had an analytical composition of 32.38 weight percent SiO 63.18 weight percent Zr0 and 3.92 weight percent V O The commercially available stain can also be prepared according the the patent references set forth supra. The concentration of the components in this latter calcined zirconia vanadia silica stain exhibits a concentration of zirconia of about twice the concentration of silica. The coefficient of expansion of the glass after the addition of the stain as measured on the divitrified glass is about 96 X 10- /C (0-300C).

EXAMPLE 3 A lead-zinc-borate sealing glass having a theoretical analysis of 2.0 weight percent SiO 8.4 weight percent B 0 74.8 weight percent PbO, 12.8 weight percent ZnO and 2.0 weight percent BaO was prepared by mixing 15.3 ounces of Ottawa Sand No. 290, 552 ounces of red lead, 62.3 ounces of boric anhydride, 88.3 ounces of zinc oxide, and 19.5 ounces of barium carbonate. The mixture was melted in an electrically heated furnace in a platinum crucible. The melting and fining procedures were conducted at 2400 to 2500F., usually about 2450F. for about 30 to 60 minutes, usually about 45 minutes. This glass was poured, fritted and ground to about 140 mesh size by conventional techniques. The sealing glass prepared from this batch and having the compositional range set forth above has a coefficient of expansion of about 103 X 10 /C (O300C).

EXAMPLE 4 A novel lead-zinc-borate sealing glass of the subject invention was next prepared as follows: to grams of the ground sealing glass prepared according to Example 3 was added 2.5 grams of the calcined zirconia vanadia silica stain. The proportion of the SiO to ZrO to V 0 in the commercially available l-larshaw Company stain was 3 to 6 to 0.3. The expansion of this glass is about 96.7 X 10 /C (0300C).

EXAMPLE 5 The following table sets forth lead borosilicate and lead-zinc-borosilicate sealing glass in percent by weight to which from 2 to 18% of the calcined zirconia vanadia silica stain can be added to give typical thermally crystallizable sealing glasses:

Each of these glasses, identified as 5 through 8 inclusive, may be used as a base glass for intimately mixing with the calcined zirconia vanadia silica stain. For example, separate composition of matter was formulated consisting of glass number 5 to which was added 5%, 7%, 8% and 8.5% of the the calcined stain. To base glass number 6 was added 5 of the calcined stain, to base glass number 7 was added 2.5, 5 and 15% of the calcined stain, and, to base glass number 8 was added 8, l2 and 16% of the calcined stain. All of the stains and glasses were intimately blended to form a homogeneous uniform composition of matter. The calcined zirconia vanadia silica stain emmployed in Examples 5 through 9 was the commercially available Harshaw Chemical Co. stain. The stain had a chemical analysis of 32.38% SiO 63.18% ZrO 3.92% V and a physical analysis demonstratiiig an average particle size of 9.7 microns, with an average range of 80% of the particles between 1 and 20 microns, usually between 4.4 to 16.8 microns. The emission spectrographic analysis shows a SiO major (greater than 10%), ZrO major (greater than 10%) and V 0 major (greater than 10%). Tile crystals in the stain appear mainly as tabular prisms, and the stain crystals are pleochloric.

The sealing glass compositions of the instant invention are employed as sealing glasses for assembling glass, ceramic, or metal parts by conventional methods known to the art. The sealing glasses can be applied by hot and cold techniques. When the cold procedure is employed, the sealing glasses are ground and mixed with a suitable vehicle to form a paste. One acceptable vehicle is made of about 1 to 3%, usually about 1 to 2% nitrocellulose in amyl acetate. Other acdeptable or ganic binders or vehicles may be employed provided they will readily burn off and volatilize during the heating procedure of the sealing of the preformed glass, ceramic or metal part. In addition, the organic binder should not react with any of the elements making up the bonded assembly. Examples of other organic binders which can be used include gelatin dissolved in water, nitrocellulose and butylacetate, camphor with cellulose, and the like.

The sealing glass composition, mixed with the vehicle can bemanually or mechanically applied by using a spatula, extrusion, cold dip, brush, roller coat, spray, doctor blade or any other like means. In the extrusion technique, which is usually employed for sealing a cathode ray tube face plate to its funnel, a toothpaste-like mixture of solder glass and carrier can be used to hold and dispense a uniform layer along the sealing edges of the respective parts.

After coating, with the sealing glass compositions of the instant invention and employing any of the sealing techniques discussed supra, the coated parts can be dried in an oven or by any suitable heating procedure. The dry assembled parts are then intimately bonded in an oven and finally cooled to room temperature.

While the above-detailed description is seen to illustrate the application of the sealing glass composition before the heating step, it is to be understood that the preformed parts to be assembled could be preheated, dipped and then fired.

Generally, when the hot method of application is employed, the solder glass composition is first melted in a suitable container, such as a platinum or fused silica crucible or the like, to a temperature above the working point followed by dipping the preheated, preformed parts into the molten solder glass and then allowing the assembly to set for a few seconds. After the thus treated parts have slightly cooled, they are aligned for assembly and sealed in an oven heated to the sealing temperature.

The above examples are illustrative of sealing techniques, and it is to be understood that the sealing procedures disclosed herein are not intended to limit the instant disclosure, as other techniques will be obvious to those versed in the subject art.

The following examples are illustrative of the present invention and they are not to be considered as limiting the spirit and scope of the invention in any manner, as these and other variations will be readily apparent to those versed in the subject art.

EXAMPLE 6 Typical sealing glasses as dispersed in a carrier were prepared as follows: to 10 gram amounts of the sealing glasses as prepared according to the procedure as set forth in Examples l5 were incorporated in about l /2% nitrocellulose in amyl acetate as described according to the discussion as set forth immediately above.

EXAMPLE 7 The present examples demonstrate the effectiveseals that are uniformly obtained by using the novel composite sealing glasses of this invention. Color television funnels were sealed to color television faceplates by applying a sealing glass composition consisting of 79.5 weight percent PbO, 10 weight percent ZnO, 7.7 weight percent B 0 2.3 weight percent SiO and 0.5 weight percent K 0 having intimately dispersed therein 8 percent of calcined zirconia vanadia silica stain. This homogeneous blend was dispersed in a standard nitrocellulose amyl acetate vehicle, as set forth in Examples 1, 2 and 6 supra. After the first sealing glass was extruded onto the sealable surfaces, it was air dried for about 2 hours. The funnels and faceplates were next placed on a sealing rack and sealed in a conventional recirculating surface combustion oven. The furnace was gas fired. The sealing cycle consists of raising the heat at a rate of 10C. per minute from room temperature to 425C., holding'the temperature at 425 for 60 minutes, then cooling to 250C. at a rate of 5C. per minute and finally to room temperature. The faceplate has a coefficient of expansion of 98.5 X 10 .C (0300C) and the funnel had a coefficient of expansion of 98.5 X 10 C (0300C). The firmly sealed faceplate to funnel composites were tested for conventional stress measurements by sectioning a cut from the bulb and measuring the stress in pound per square inch at the center of the sectioned sample. The stress readings for the section as read at 3:00, 6:00, 9:00 and 12:00 for the faceplate was 285 C, 245 C, 290 C and 330 C. For the funnel the stress was 245 C, 335 C, 420 C and 415 C respectively. The glasses used to make the faceplate and the funnel are commercially available glasses. The composition of the faceplate glass is, in weight percent, as follows: 63.5 SiO 4.4 A1 0 10.3 K 0; 7.3 Na O; 5.2 Ca0 MgO; 7.5 BaO; 0.1 PbO; 0.1 AS203; and Sb O 0.3. The composition of the glass used for making the funnel is, in weight percent, as follows: 59.2 SiO 4.1 A1 0 7.3 K 0; 7.4 Na O', 4.8 CaO; 3.2 MgO; 1.8 BaO; 9.4 PbO; 0.1 As O 0.2 Sb O 1.8 Rb2O; and 0.5 Li O. The letter C in the a gradient furnace having a temperature range of 950' to 1950F. over a 10 inch span boat. A teninch boat is filled with a fritted glass and placed into the furnace for one hour. The temperature is measured at about 1 inch intervals over the boat every 5 minutes before removal to establish the temperature gradient. After cooling, the glassy and crystal edges of the sample are measured and recorded. This test indicates the primary flow range of the sealing glass, which is from glassy to crystallization edge.

The button flow test was employed to determine the flow characteristics of a given crystallizable solder glass. The button flow test aids in demonstrating the filleting properties of the glass which can be related to actual seal filleting. The test consists essentially of making ten-grain pressed cylinders or pellets of solder glass with a diameter of inch under a pressure of about 1000 psi, placing each pellet or cylinder in the center of a glass plate 2 X 2 X A inches and heating said button in a furnace until the temperature stabilizes at 150F. with a temperature rise of 7to 10C. per minute to 425to 450C, holding the temperature at 425 to 450C. for 60 to 70 minutes, and then cooling at a rate of 1C. per minute to 330C. The diameter of the heat treated finally cooled button is measured and compared against buttons of a standard similarly treated glass button fired at the same time.

A sea] stress test was conducted to determine if the glasses can be satisfactorily processed without breakage due to high seal stress. The test was conducted by cutting a piece of base glass into one inch sections and one end of two sections were ground, polished, annealed and wiped with acetone. A small pellet of solder glass, formed in a pellet die, was placed on one end of each glass section and a drop of the nitrocellulose in amyl acetate vehicle was placed on top of the pellet. The seals were made by heating in an electric oven at 425 to 450C. for 60 to 70 minutes with a temperature use to said temperature of 10C. per minute. The sealed samples were cooled at the rate of 5C. per minute. The seal stress was read in a polarimeter and calculated to psi. The readings and calculations were made in the base glass. The base glass is a commercially available glass consisting of 63.5 weight percent SiO 4.4 weight percent A1 0 10.3 weight percent K 0, 7.3 weight percent Na 0, 52 weight percent Ca0 MgO, 0.3 weight percent Sb 0 7.5 weight percent BaO and 0.1 weight percent PbO. The stress in the solder glass is found by reversing the direction of the psi values.

The differential thermal analysis, D.T.A., was made by heating a 100 mg. sample in a conventional, commercially available duPont 900 Differential Thermal Analyzer. The analysis is performed as follows: A sample, usually about 100mg. in weight, is placed into a small glass vial and is then inserted into the sample contained in said vial to record the temperature of the sample.

In a similar vial are placed glass beads that are inert over the testing temperature range; and, into these beads is placed a similar thermocouple to control the rate at which the temperature rises. Next, heat is applied to the glass beads so that they are heated at a rate of 10C. per minute. The two vials are heated simultaneously and uniformly by the same heat source. Any possible reactions that may occur within any material manifest either an exothermic or endothermic behavior. Therefore, when a reaction occurs in the test sample, the thermocouple records the difference of the temperature of the test sample and that of the con trolled glass beads. The differences that occur are recorded on a chart and this produces what is known as a D.T.A. curve. This curve demonstrates the exothermic and endothermic reactions that have occurred within the test sample over the selected temperature range.

The results of the various tests discussed supra are set forth in the table immediately below. In the table, composition A is a novel sealing glass consisting of 79.5 weight percent PbO, 10.0 weight percent ZnO, 7.7 weight percent B 0 2.3 weight percent SiO and 0.5

weight percent K 0 having homogeneously dispersedtherein 8 percent of calcined zirconia vanadia silica stain. The homogeneous composition was intimately dispersed in a standard nitrocellulose amyl acetate vehicle. The preparation of this glass and its vehicle are set forth in Examples 1, 2 and 6. In the table, glass B has the same composition as glass A, with the exception that glass B does not contain any calcined zirconia vanadia silica stain dispersed with glass B. The glass identified as glass C has the following ingredients: 74.99 weight percent PbO, 12.96 weight percent ZnO, 8.26 weight percent B 0 2.10 weight percent SiO 2.03 weight percent BaO and 2.5 percent of the calcined zirconia vanadia silica stain homogeneously and intimately blended throughout said sealing glass. TI-Ie glass labeled as D is the same as glass C, except that there is no calcined stain in glass D. In this table. D.T.A. is an abbreviation for Differential Thermal Analysis, PSI for pounds per square inch, C for compression, and T for tension.

DESCRIPTION OF THE DRAWINGS In the accompanying FIG. 1, the stress is depicted in a sealing glass consisting essentially of 2.3 weight percent SiO 7.7 weight percent B 0 10 weight percent ZnO, 79.5 weight percent PbO and 0.5 weight percent K 0 with varying percents of calcined zirconia vanadia silica stain added to the sealing glass composition. The

sealing glass was firmly sealed to a glass rod with a di ameter of about /2 inch and cured at 425C.

FIG. 2 shows the thermal expansion, illustrated as tension, of a second sealing glass with the following composition, 3.5 weight percent SiO 7.5 weight percent B O 6.3 weight percent ZnO, 80.6 weight percent PbO and 2.1 weight percent BaO is lowered when the calcined zirconia vanadia silica stain is added in various concentrations to the sealing glass composition. The glass used as the rod to which the seals were made has a composition of 70.6 weight percent SiO 0.2 weight percent B 2.0 weight percent A1 0 0.3 weight percent K 0, 13.4 weight percent Na O, 7.2 weight percent CaO, 5.3 weight percent MgO, and 1.0 weight percent BaO. The sealing temperature for the second sealing glass was effected at 380C. The data presented herein indicates that unobvious flow properties, complete crystallization in less than 60 minutes at lower temperatures and a lowering of the thermal expansion are obtained for the novel compositions of this invention. The sealing glass produces, in addition to the other desirable properties set forth above, strong seals and good electrical properties.

The sealing glass compositions of the present invention can be employed to manufacture items of science and commerce. For example, the sealing glasses are ideally suited for sealing television color tubes because the sealing glass cures at 425 i C., which cure property is needed for sealing color tubes. The subject glasses as shown in FIG. 1 cure about 20 lower than the presently available sealing glasses. Additions of ca]- cined stain lower the crystallization temperature of sealing glasses from 10 to C. The sealing glasses can also be used for joining metallic alloys to glass parts in the fabrication of electronic components, for joining glass to ceramics and the like.

While the illustrative embodiments of the invention have been described with particularity, it will be under stoodo that various modifications will be apparent and can readily be made by those skilled in the art without departing from the scope and spirit of the invention.

1 claim:

1. An improved thermally crystallizable fusion-type sealing glass composition of matter wherein said composition consists essentially of a base sealing glass selected from the group consisting essentially of leadzinc-borate and lead-borosilicate sealing glasses and wherein said base sealing glass has homogeneously blended therein about 2 to 18 percent by weight of a calcined zirconia vanadia silica stain, said resulting fusion-type sealing glass having therby a thermal coefficient of expansion in the devitrified state ranging from about 5 X l0 /C (O-300C) to 20 X lO' /C (0-300C) lower than the same glass in the devitrified state would have in the absence of the calcined zirconia vanadia silica stain.

2. The improved sealing glass composition according to claim 1 wherein the calcined stain lowers the crystallization temperature of the sealing glass 10 to 15C.

3. The improved sealing glass composition according to claim 1 wherein said lead-zinc-borate sealing glass consists essentially of to weight percent PbO, 6 to 15 weight percent ZnO, 7; to 10 weight percent B 0 and 0 to 5 weight percent Si0 and the lead borosilicate sealing glass consists essentially of 70 to 85 weight per cent PhD, 7 to 15 weight percent B 0 2 to 10 weight percent SiO and l to 5 weight percent A1 0 4. The improved sealing glass composition acccording to claim 1, wherein said base sealing glass has homogeneously blended therein about 8% by weight of a calcined zirconia vanadia silica stain.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 888, 686

DATED June 10, 1975 INVENTOR(S) J. L. Ellis It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: G

In Fig. 2 of the drawings, under the heading "ROD SEAL STRESS P.S.I. TENSION IN SEALING GLASS", the number "000" should be -lO0O-; Col. 1, line 37, "or" should be of-Col. 4, line 13, "the" (first occurrence) should A be ---to; C01. 5, line 13, "emmployed" should be -employed-; line 23, "TI-1e" should be -'-The-; line 33, "acdeptable" should be acceptable; Col. 8, line 38,

"THe" should be -'The-; Col. 10, lines 2 and 3, "understoodo" should be -understood--; line 15, "therby" should be -thereby--.

or Signed and Sealed this Twenty-fourth D8) Of May 1977 [SEAL] A ttest: J

RUTH C. MASON C. MARSHALL DANN 8 /1 Commissioner oj'Parems and Tradvmarks 

1. AN IMPROVED THERMALLY CRYSTALLIZABLE FUSION-TYPE SEALING GLASS COMPOSITION OF MATTER WHEREIN SAID COMPOSITION CONSISTS ESSENTIALLY OF A BASE SEALING GLASS SELECTED FROM THE GROUP CONSISTING ESSENTIALLY OF LEAS-ZINC-BORATE AND LEAD-BOROSILICATE SEALING GLASSES AND WHEREIN SAID BASE SEALING GLASS HAS HOMOGRNEOUSLY BLENDED WHEREIN ABOUT 2 TO 18 PERCENT BY WEIGHT OF A CALCINED ZIRCONIA VANADIA SILICA STAIN, SAID RESULTING FUSIONTYPE SEALING GLASS HAVING THEREBY A THERMAL COEFFICIENT OF EXPANSION IN THE DEVITRIFIED STATE RANGING FROM ABOUT 5X10**-7/*C (0*-300*C) TO 20X10**-7/*C (0*-3000*C) LOWER THAN THE SAME GLASS IN THE DEVITRIFIED STATE WOULD HAVE IN THE ABSENCE OF THE CALCINED ZIRCONIA VANADIA SILICA STAIN.
 2. The improved sealing glass composition according to claim 1 wherein the calcined stain lowers the crystallization temperature of the sealing glass 10* to 15*C.
 3. The improved sealing glass composition according to claim 1 wherein said lead-zinc-borate sealing glass consists essentially of 70 to 85 weight percent PbO, 6 to 15 weight percent ZnO, 7; to 10 weight percent B2O3 and 0 to 5 weight percent SiO2 and the lead borosilicate sealing glass consists essentially of 70 to 85 weight percent PbO, 7 to 15 weight percent B2O3, 2 to 10 weight percent SiO2 and 1 to 5 weight percent Al2O3.
 4. The improved sealing glass composition acccording to claim 1, wherein said base sealing glass has homogeneously blended therein about 8% by weight of a calcined zirconia vanadia silica stain. 